1. Field of the Invention
The present invention discloses a safety valve which is manually operated. The present invention can be installed in drill strings and/or workover strings used in oil and gas wells.
2. Description of the Prior Art
While drilling an oil or gas well, the downhole pressure of formation fluids is normally controlled by circulating drilling mud through the well bore. The normal mud flow path is down through the bore of the drill string and up the annulus between the exterior of the drill string and the inside diameter of the well bore. Various types of blowout preventers are available to seal against the exterior of the drill string at the well surface to prevent undesired formation fluid flow from the annulus.
Formation fluids may also flow upward through the bore of the drill string if the downhole pressure of the formation fluid exceeds the hydrostatic pressure of the drilling mud.
U.S. Pat. No. 3,036,590 to Granville S. Knox discloses a manually operated valve which can be installed in the drill and/or tubing string at the well surface. As noted in U.S. Pat. No. 3,036,590, the outside diameter of this valve is enlarged with respect to the tubing string in which the valve is connectable. U.S. Pat. No. 3,036,590 is incorporated by reference for all purposes within this application.
U.S. Pat. No. 3,743,015 discloses a mud saver valve which functions as a check valve to prevent reverse flow up the bore of the drill string. The mud saver valve is not manually operated between its open and closed positions. The mud saver valve can be manually locked open if desired.
U.S. Pat. No. 4,074,761 discloses a safety valve which can be stabbed or connected onto the open end of a drill string at the well surface. The safety valve is mechanically locked open during the stabbing process and is moved to its closed position by a spring and/or fluids flowing in the reverse direction through the drill string.
U.S. Pat. No. 3,273,588 to W. W. Dollison discloses an operating sleeve moving longitudinally within a housing to shift various types of valve closure means such as a ball member, a flapper, or a poppet between their open and closed positions, U.S. Pat. No. 3,273,588 is incorporated by reference for all purposes within this application.